FRANKFURT. While stuttering was believed to have purely psychological causes up until about 30 years ago, scientists today attribute it to a variety of factors capable of contributing to its development. For instance, several genes have been identified that increase the risk of stuttering, and anatomically, the brains of individuals with speech flow disorders show differences in neural connections and brain activity compared to those who speak fluently.

PD Dr. Christian Kell, neurologist and director of the Cooperative Brain Imaging Center at Goethe University Frankfurt, explains: “The left hemisphere of the brain can process signals that occur in rapid succession. However, in people who stutter, the auditory cortex in the left hemisphere interacts less with the motor cortex, which controls the muscles involved in speech. As a result, the brain may delegate these tasks to the right hemisphere, which struggles with the rapid signals characteristic of speech.” The outcome: Although affected individuals know exactly what they want to say, they get stuck on certain words.

Kell does not consider stuttering to be a disease that necessarily requires therapy: “I believe it would be ideal if society could accept that some people stutter,” says the neurologist. At the same time, he is convinced that medicine should offer services to those who suffer from their speech flow disorder and seek help.

Following extensive scientific preparation and at the patient’s repetitive request, the teams from Frankfurt and Münster implanted a hair-thin wire into the left thalamus of a man who stutters. The thalamus is a central relay station deep within the brain. Through this wire, the brain region was stimulated with mild electrical currents. Standardized tests were then used to measure how the patient’s stuttering changed.

Kell is thrilled with the results: “In the months following the start of stimulation, the frequency of stuttering gradually decreased by 46%, and the stuttering became significantly less severe. When we turned off the deep brain stimulation without the patient knowing the timing, the stuttering worsened again, demonstrating a genuine biological effect dependent on the strength of the brain stimulation.” Unlike Parkinson’s patients, whose tremors typically diminish immediately after starting brain stimulation and return as soon as the stimulation is stopped, the stuttering in this case increased very slowly after the stimulation was turned off – but not to the same extent as before. Kell attributes part of this effect to the patient himself: “Through the experience of stuttering less during stimulation, he and his brain likely found ways to further reduce the stuttering.”

The research team is now preparing a study to investigate whether deep brain stimulation can also help other individuals who experience severe stuttering. However, Kell is careful to curb overly high expectations: “Deep brain stimulation is an intensive physical procedure and, like any surgery, carries risks. These must be carefully weighed against the distress experienced by a person who stutters. We also want to explore whether we can achieve similar effects by stimulating the brain externally – without surgery.”